There are currently an estimated 40,000 incidences of cardiac arrest every year in Canada, most of which take place outside of hospital settings. The odds of an out-of-hospital cardiac arrest currently stand at approximately 5%. In the U.S., there are about 164 600 such instances each year, or about 0.55 per 1000 population. There is a desire to decrease these out-of hospital incidences of cardiac arrest. Certain places, such as sports arenas, and certain classes of individuals, such as the elderly, are at particular risk and in these places and for these people, a convenient solution may be the difference between survival and death.
Cardiopulmonary resuscitation (CPR) is a proven effective technique for medical and non-medical professionals to improve the chance of survival for patients experiencing cardiac failure. CPR forces blood through the circulatory system until professional medical help arrives, thereby maintaining oxygen distribution throughout the patient's body. However, the quality of CPR is often poor. Memory retention of proper CPR technique and protocol may be inadequate in most individuals and the anxiety of an emergency situation may confuse and hinder an individual in delivering proper treatment.
According to the journal of the American Medical Association (2005), cardiopulmonary resuscitation (CPR) is often performed inconsistently and inefficiently, resulting in preventable deaths. Mere months after the completion of standard CPR training and testing, an individual's competency at performing effective chest compressions often deteriorates significantly. This finding was found to hold true for untrained performers as well as trained professionals such as paramedics, nurses, and even physicians.
The International Liaison Committee on Resuscitation in 2005 described an effective method of administering CPR and the parameters associated with an effective technique. Parameters include chest compression rate and chest compression depth. Chest compression rate is defined as the number of compression delivered per minute. Chest compression depth is defined as displacement of the patient's sternum from its resting position. An effective compression rate may be 100 chest compressions per minute at a compression depth of about 4-5 cm. According to a 2005 study at Ulleval University Hospital in Norway, on average, compression rates were less then 90 compressions per minute and compression depth was too shallow for 37% of compressions.
According to the same study, CPR was often administered when unnecessary or was not administered when necessary. The study found that compressions were not delivered 48% of the time when cardiovascular circulation was absent.
Positioning of the hands is another parameter that may be considered when delivering CPR. It has been found that an effective position for the hands during compression is approximately two inches above the base of the sternum. Hand positioning for effective CPR may be different depending on the patient. For example, for performing CPR on an infant, an effective position may be to use two fingers over the sternum.
Other studies have found similar deficiencies in the delivery of CPR. A 2005 study from the University of Chicago found that 36.9% of the time, fewer than 80 compressions per minute where given, and 21.7% of the time, fewer than 70 compressions per minute were given. The chest compression rate was found to directly correlate to the spontaneous return of circulation after cardiac arrest, so it is very important that the optimum rate be achieved for maximum chances of patient survival.
In addition to too shallow compressions, too forceful compressions may also be problematic. Some injuries related to CPR are injury to the patient in the form of cracked ribs or cartilage separation. Such consequences may be due to excessive force or compression depth. Once again, lack of practice may be responsible for these injuries.
Therefore, a device to facilitate the proper delivery of CPR in an emergency is desired. Furthermore, a device that can also be used in objectively training and testing an individual may be useful for the CPR training process and protocol retention.
Current solutions in emergency cardiac care mostly focus on in-hospital treatment or appeal mostly to medical professionals. CPR assist devices that tether to defibrillators can be found in hospitals. However, these devices are often expensive and inaccessible to the lay individual who does not have a defibrillator on hand or cannot operate such a device. Furthermore, such devices are often not portable nor are they easily accessible. Simple devices with illuminated bar graph or LED displays indicating compression force are often cumbersome in design and non-intuitive in use. Such a device may be uncomfortable to the patient and user and often has minimal data output. Thus, misuse of such a device is most likely rendering it a hindrance rather than an aid.
There are currently mechanical systems for the delivery of CPR that may be used in a hospital setting. Chest compression may be delivered through a mechanism including mechanical movement (e.g., piston movement or motor movement). One such device is the AUTOPULSE by Revivant Corp, which has a computer-controlled motor attached to a wide chest band that compresses the chest, forcing blood to the brain when the heart has stopped beating. Such a device is cumbersome and heavy to transport, requires time to set up and activate and is expensive.
U.S. Pat. No. 6,351,671 discloses a device that measures the chest impedance of a victim as well as the force of active chest compressions. From these calculations, the device indicates to the user when a successful compression has been completed. However, this technology requires defibrillator pads to be placed across the chest of the victim and is, consequently, relatively time consuming to activate. The commercially available device, Q-CPR by Phillips Medical, must be attached to an expensive hospital-grade defibrillator making it expensive, heavy and inaccessible to the lay user.
U.S. Pat. No. 7,074,199 discloses the use of an accelerometer for the measurement of compression depth. Any acceleration data from accelerometers used to measure the depth of chest compression during CPR is prone to cumulative errors. Consequently, these sensors are not suitable for highly accurate or detailed data collection regarding CPR parameters and can only be relied on for approximate depth values. Furthermore, the use of an accelerometer in a CPR monitoring device without an external reference is prone to error if the patient or rescuer is mobile. For example, if the patient is being medically transported in an ambulance, helicopter or on a gurney, the accelerometer is unable to differentiate between the external movement of the patient and the compressions of the chest. In any type of non-stationary environment, an accelerometer based device is unreliable and ineffective. The use of an accelerometer to calculate compression depth also relies on complicated and error-prone calculations to compensate for the angle and tilt of the compression device. If the accelerometer is not perfectly level on the chest of the victim and its movement is not perfectly vertical, errors will accumulate and must be accounted for by the angle of the two horizontal axes. Certain commercial products currently use accelerometer technology, such as the AED PLUS D-PADZ from Zoll Medical, in which the accelerometer is embedded into the pads of the defibrillator. Due to the additional circuitry and sensory within them, these defibrillator pads are substantially more expensive and must be disposed of after each use. Therefore, relatively expensive sensory must be routinely discarded due to the design of the product.
Currently, a widely used technology in the training environment is the CPR mannequin. One commonly used version is the RESUSCI-ANNE doll manufactured by Laerdal Medical Inc. The RESUSCI-ANNE doll allows an individual to practice his or her CPR while being subjectively monitored by an instructor. This technique relies on the observational skills of the instructor and thus may be prone to human error. Furthermore, for effective training to take place, each student must be observed separately thereby occupying a significant amount of time and decreasing the number of students who can be trained at one time. In addition, Actar Airforce Inc. develops ACTAR mannequins providing limited feedback that are currently also used in CPR training. Again, such mannequins rely on close monitoring by the instructor to be effective for training.
It would still be desirable to provide an easy-to-use and inexpensive device to accurately measure relevant CPR parameters such as compression depth and rate absent of the problems in the aforementioned technologies.